1. Field of the Invention
The present invention relates to a composition for treating human hair comprised of a thiol compound that is a superior hair reductant and hair cosmetic especially in terms of waving effect, odor, hair damage, texture and safety.
The present invention also relates to a method of treating human hair using this composition.
2. The Prior Art
Hair reductants currently used in Japan are ammonium thioglycolate calciumthioglylate and cysteine.
Of these, primary agents for permanent waving (hereafter referred to as "primary agents for permanents") which contain ammonium thioglycolate have the characteristic of giving a strong wave effect.
However, these primary agents for permanents have the following shortcomings:
1. The degree of hair damage is high and the hair texture tends to deteriorate.
2. Skin irritation may result if the manner of preparation or use of the liquid agents are improper.
3. There is an offensive odor characteristic of permanent agents which is caused by the thioglycolic acid.
Although much effort has been put towards solving these shortcomings, currently they have not been solved.
On the other hand, it is believed that primary agents for permanents which contain cystsine cause less hair damage and in general cause less skin irritation and have a less offensive odor at room temperature.
However, these primary agents for permanents have the following shortcomings:
1. The waving effect is weak. Since the waving effect is weak, a means such as strengthening the alkalinity with liquid agent formulas is likely to be used, resulting in possible skin irritation caused by alkalinity.
2. Cysteine is not stable, so that when the liquid agent is old or exposed to high temperatures the cystsine content decreases and, at the same time, a considerable amount of hydrogen sulfide is generated as a byproduct, resulting in the offensive odor problem characteristic of permanents.
Currently, these shortcomings have not yet been overcome. Recently, another type of hair cosmetics, those which contain sulfides and such as hair reductants, have begun to be commercially sold.
Their features include very little of the offensive odor characteristic of permanents and a high degree of safety against hair damage and skin irritation.
However, these hair reductants have the following serious problems:
1. Since their reducing action on the hair is so weak, the heated hair curling cosmetics, for example, used by heating up to 60.degree. C. or less, require prolonged heat treatment because of the weak curling. Also, in the case of cosmetics for frizzy hair and cosmetics for hair softening, a one-time treatment hardly produces an effect and thus on-going use is required.
By the way, Calcium thioglycollate is a reducing agent for human hair which is currently used in Japan as a hair remover for the removal of unwanted hair (body hair) from arms and legs.
A hair remover containing calcium thioglycollate softens and removes unwanted hair (body hair) from arms and legs. However, it has the following shortcomings.
(1) Since the hair remover must have a strongly alkaline pH of 11-12, it is very hard on skin of arms and legs. If the recipe or usage is not appropriate, it may lead to skin irritation and thus cause problems.
(2) The characteristic offensive odor arising from thioglycollic acid is not desirable.
Also, in general, since an acidic hair dye has a weak dyeing power particularly on healthy gray hair, it is known: that treating the hair with an alkaline solution such as ammonium thioglycollate and cysteine before the acidic hair dye treatment improves the dyeing result somewhat. However, there are problems as follows:
(1) The characteristic offensive odor arising from thioglycollic acid is not desirable, and
(2) Since the pretreatment before dyeing is conducted at an alkaline pH and the acidic hair dye is acidic, efficiency is low.
In this current situation, the inventor wholeheartedly searched for and evaluated various new reductants. As a result, we have found hair reductants which are superior to conventional thioglycolate and cysteine in terms of waving effect, hair-removing effect, improving of dyeing effect, odor, hair damage, texture, safety, etc.